Prior art filters include housings around filter elements, and some include cleaning elements mounted inside the housing to periodically remove debris and contaminants from the filter elements. Examples of prior art systems and methods are illustrated in FIGS. 1A and 1B. Generally, dirty water or other fluid enters the assembly through a “dirty” inlet, passes into the central portion of the filter assembly, and then is filtered by passing radially outwardly through a cylindrical filter element. During use, the high pressure filtering area is “separated” from a lower pressure flushing portion of the assembly by a divider or separating bulkhead.
In these devices, when the filter becomes clogged or too dirty, a valve on the flush outlet is opened to “clean” or “vacuum” the filter. The valve can be actuated, for example, when the system reaches a predetermined pressure differential between the dirty inlet and the clean outlet. The differential typically is monitored by sensors, and that differential typically increases as filtered materials collect on the inside of the filter element.
In systems such as illustrated in FIGS. 1A and 1B, the vacuum cleaning is provided by relatively low pressure at the flush outlet (when the flush valve is opened). That low pressure communicates through a motor assembly connected to vacuum rotors. The rotor inlets are positioned close to the filter element. The relatively lower pressure at the flush outlet creates a vacuum that sucks the debris or buildup formed on the inside of the filter back through the vacuum rotors, back out the motor assembly, and finally through the flushing/cleaning outlet. The aforementioned fluid flow generates a thrust on the motor assembly outlets that rotates the motor and the entire assembly connected to it. The rotating assembly includes the vacuum rotors, which (by rotating) pass over and “vacuum clean” at least some portion of the interior surface of the filter element.
Prior art systems have several shortcomings. Among other things, although systems such as illustrated in FIG. 1A have vacuum rotors sized and positioned to cover substantially all of the filter surface within a single 360 degree rotation, those rotors require large valves and correspondingly large fluid flow to provide sufficient vacuum suction to clean the filter satisfactorily.
Systems such as FIG. 1B typically use smaller valves, but do not provide a “controlled” cleaning cycle that reliably cleans the entire surface of the filter. Instead, the vacuum rotors and motor assembly of FIG. 1B not only rotate during cleaning but also traverses axially from a right-most position (such as shown in FIG. 1B) to the left (not shown). A tight fit 25 is provided between the separating bulkhead and the motor assembly, that permits the motor to rotate within the bulkhead but also permits a “bleed” of pressure past the tight fit 25. When the flush outlet is opened, the high-pressure area adjacent the filter can gradually bleed through the tight fit into the low-pressure area, eventually equalizing those two pressures. Until the pressures equalizes, however, the higher pressure tends to force the motor/rotor assembly to the left.
That movement to the left is impeded to some degree by relatively incompressible fluid in a cylinder 20. To permit some movement to the left, the opening of the flush outlet is coordinated with opening a tiny bleed port 28 at the end of a cylinder 20. That opened bleed port 28 permits a piston 22 in the cylinder 20 (which piston is connected to the motor/rotor assembly) to move toward the left as water is forced out the bleed port 28.
Once the pressure has equalized, the flush outlet and bleed port 28 are closed, and the larger effective surface area on the left side of the motor/rotor assembly forces the assembly to move back to the right. During that portion of the cycle, there is no vacuum action at the rotor inlets, so the filter is not being cleaned. Said another way, the only “cleaning” that occurs is during the single pass from right to left. Depending on the pressure differential, the condition of the various seals and fitting areas, and other factors, that single pass movement from right to left can occur so quickly that it is uncertain that the rotor inlets will pass over all of the filter's interior surface. Those areas that are missed remain dirty, decreasing efficiency and performance of the filter, and requiring more frequent (albeit less efficient) cleaning cycles.